Method for transmitting a power headroom reporting in a carrier aggregation with at least one scell operating in an unlicensed spectrum and a device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting a power status reporting in a carrier aggregation with at least one SCell operating in an unlicensed spectrum, the method comprising: receiving, by a MAC entity, an uplink grant to transmit data on an unlicensed cell from an eNB; checking, by the MAC entity, whether the unlicensed cell is available for transmitting the data using the uplink grant; determining, by the MAC entity, not transmitting the data using the uplink grant if the unlicensed cell is not available for transmitting data; and triggering, by the MAC entity, a PHR when the UE determines that the data is not to be transmitted.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting a power headroomreporting in a carrier aggregation with at least one SCell operating inan unlicensed spectrum and a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for transmitting a power headroom reporting in acarrier aggregation with at least one SCell operating in an unlicensedspectrum.

The technical problems solved by the present invention are not limitedto the above technical problems and those skilled in the art mayunderstand other technical problems from the following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for User Equipment (UE) operating in a wireless communicationsystem as set forth in the appended claims.

In another aspect of the present invention, provided herein is acommunication apparatus as set forth in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

According to the present invention, if the UE drops data transmission ona cell not due to power limitation situation, the UE triggers the powerheadroom reporting in order to inform the eNB of power situation.

It will be appreciated by persons skilled in the art that the effectsachieved by the present invention are not limited to what has beenparticularly described hereinabove and other advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention;

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure;

FIG. 7 is a diagram for exemplary Licensed-Assisted Access (LAA)scenarios;

FIG. 8 is an example of LBT operation of a Frame Based Equipment (FBE)

FIG. 9A is an illustration of the CCA check procedure for FBE; and FIG.9B is an illustration of the CCA check and backoff procedures for LBE.

FIG. 10A is a diagram for State Transition Diagram for a LAA eNB, FIG.10B is a diagram for Passive State operations for FBE and LBE, FIG. 10Cis a diagram for Active State operations for LBE, and FIG. 10D is adiagram for Active State operations for FBE.

FIG. 11 is a diagram for signaling of buffer status and power-headroomreports; and

FIG. 12 is a conceptual diagram for transmitting a power headroomreporting in a carrier aggregation with at least one SCell operating inan unlicensed spectrum according to embodiments of the presentinvention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan ×2 interface and neighboring eNodeBs may have a meshed networkstructure that has the ×2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprises a DSP/microprocessor(110) and RF module (transceiver; 135). The DSP/microprocessor (110) iselectrically connected with the transceiver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure.

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 6(a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 6(b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 6(b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≦N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≦M≦N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher-layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

FIG. 7 is a diagram for exemplary Licensed-Assisted Access (LAA)scenarios.

Carrier aggregation with at least one SCell operating in the unlicensedspectrum is referred to as Licensed-Assisted Access (LAA). In LAA, theconfigured set of serving cells for a UE therefore always includes atleast one SCell operating in the unlicensed spectrum, also called LAASCell. Unless otherwise specified, LAA SCells act as regular SCells andare limited to downlink transmissions in this release.

If the absence of IEEE802.11n/11ac devices sharing the carrier cannot beguaranteed on a long term basis (e.g., by level of regulation), and forthis release if the maximum number of unlicensed channels that E-UTRANcan simultaneously transmit on is equal to or less than 4, the maximumfrequency separation between any two carrier center frequencies on whichLAA SCell transmissions are performed should be less than or equal to 62MHz. The UE is required to support frequency separation in accordancewith 36.133.

LAA eNB applies Listen-Before-Talk (LBT) before performing atransmission on LAA SCell. When LBT is applied, the transmitter listensto/senses the channel to determine whether the channel is free or busy.If the channel is determined to be free, the transmitter may perform thetransmission; otherwise, it does not perform the transmission. If an LAAeNB uses channel access signals of other technologies for the purpose ofLAA channel access, it shall continue to meet the LAA maximum energydetection threshold requirement. The unlicensed band can be used for aWi-Fi band or a Bluetooth band.

It has been agreed that the LTE CA framework is reused as the baselinefor LAA, and that the unlicensed carrier can only be configured asSCell. The SCell over unlicensed spectrum may be downlink only orbi-directional with DL only scenario being prioritized in the SI. LAAonly applies to the operator deployed small cells. Coexistence and fairsharing with other technologies is an essential requirement for LAA inall regions.

Regarding FIG. 7, LAA targets the carrier aggregation operation in whichone or more low power SCells operate in unlicensed spectrum. LAAdeployment scenarios encompass scenarios with and without macrocoverage, both outdoor and indoor small cell deployments, and bothco-location and non-co-location (with ideal backhaul) between licensedand unlicensed carriers. FIG. 7 shows four LAA deployment scenarios,where the number of licensed carriers and the number of unlicensedcarriers can be one or more. As long as the unlicensed small celloperates in the context of the carrier aggregation, the backhaul betweensmall cells can be ideal or non-ideal. In scenarios where carrieraggregation is operated within the small cell with carriers in both thelicensed and unlicensed bands, the backhaul between macro cell and smallcell can be ideal or non-ideal.

Scenario 1: Carrier aggregation between licensed macro cell (F1) andunlicensed small cell (F3).

Scenario 2: Carrier aggregation between licensed small cell (F2) andunlicensed small cell (F3) without macro cell coverage.

Scenario 3: Licensed macro cell and small cell (F1), with carrieraggregation between licensed small cell (F1) and unlicensed small cell(F3).

Scenario 4: Licensed macro cell (F1), licensed small cell (F2) andunlicensed small cell (F3). In this case, there is Carrier aggregationbetween licensed small cell (F2) and unlicensed small cell (F3). Ifthere is ideal backhaul between macro cell and small cell, there can becarrier aggregation between macro cell (F1), licensed small cell (F2)and unlicensed small cell (F3). If dual connectivity is enabled, therecan be dual connectivity between macro cell and small cell.

In the study to support deployment in unlicensed spectrum for the abovescenarios, CA functionalities are used as a baseline to aggregatePCell/PSCell on licensed carrier and SCell on unlicensed carrier. Whennon-ideal backhaul is applied between a Macro cell and a small cellcluster in the Scenarios 3 and 4, small cell on unlicensed carrier hasto be aggregated with a small cell on licensed carrier in the small cellcluster through ideal backhaul. The focus is to identify the need ofand, if necessary, evaluate needed enhancements to the LTE RAN protocolsapplicable to the carrier aggregation in all the above scenarios.

FIG. 8 is an example of LBT operation of a Frame Based Equipment (FBE).

The Listen-Before-Talk (LBT) procedure is defined as a mechanism bywhich an equipment applies a clear channel assessment (CCA) check beforeusing the channel. The CCA utilizes at least energy detection todetermine the presence or absence of other signals on a channel in orderto determine if a channel is occupied or clear, respectively. Europeanand Japanese regulations mandate the usage of LBT in the unlicensedbands. Apart from regulatory requirements, carrier sensing via LBT isone way for fair sharing of the unlicensed spectrum and hence it isconsidered to be a vital feature for fair and friendly operation in theunlicensed spectrum in a single global solution framework.

According to ETSI regulation (EN 301 893 V1.7.1) of the Europe, two LBToperations respectively referred to as a FBE (Frame Based Equipment) andan LBE (Load Based Equipment) are shown as an example. The FBEcorresponds to an equipment where the transmit/receive structure is notdirectly demand-driven but has fixed timing and the LBE corresponds toan equipment where the transmit/receive structure is not fixed in timebut demand-driven.

The FBE configures a fixed frame using channel occupancy time (e.g.,1˜10 ms) corresponding to time capable of lasting transmission when acommunication node has succeeded in channel access and an idle periodcorresponding to minimum 5% of the channel occupancy time. CCA isdefined by an operation of monitoring a channel during a CCS slot(minimum 20 μs) at an end part of the idle period.

In this case, a communication node periodically performs the CCA in afixed frame unit. If a channel is in an unoccupied state, thecommunication node transmits data during the channel occupancy time. Ifa channel is in an occupied state, the communication node postpones datatransmission and waits until a CCA slot of a next period.

A CCA (clear channel assessment) check and backoff mechanism are two keycomponents of channel evaluation stage. FIG. 9A illustrates the CCAcheck procedure for FBE, in which no backoff mechanism is needed. FIG.9A illustrates the CCA check and backoff procedure for LBE.

In order to deploy LAA eNB in regions where LBT is required, LAA eNBshall comply with LBT requirements in those regions. In addition, theLBT procedures shall be specified such that fair sharing of theunlicensed spectrum may be achieved between LAA devices themselves andamong LAA and other technologies, e.g. WiFi.

After eNB acquires the unlicensed spectrum through LBT proceduresuccessfully, it may notify its UEs the result so that preparations maybe made accordingly for transmission, e.g., UE may start measurements.

CCA check (FBE and LBE) and backoff mechanism (LBE) are two majorcomponents of LBT operation, and thus are worth further clarification orstudy in order to fulfil LBT requirement efficiently in LAA system.Since the LBT procedure is in preparation for transmitting data orsignals over unlicensed channel, it is straightforward that both MAC andPHY layers are closely involved in the LBT process. FIGS. 10A to 10Dillustrate our views on the interaction and function split between MACand PHY during the CCA check and backoff operations. They can be used tohelp identify the potential impacts that LBT requirements brought toRAN2.

FIG. 10A is a diagram for State Transition Diagram for a LAA eNB, FIG.10B is a diagram for Passive State operations for FBE and LBE, FIG. 10Cis a diagram for Active State operations for LBE, and 10D is a diagramfor Active State operations for FBE.

An LAA eNB operating status is classified as in either Active State orPassive State, as shown in FIG. 10A.

The passive state means that an LAA eNB has no need of utilizingunlicensed channels, and the active state means that an LAA eNB is inneed of unlicensed resources. The transition from Passive State toActive State is triggered when radio resources over unlicensed channelis needed.

FIG. 10B depicts the operation in Passive State in more details, and isapplicable to both FBE and LBE. The transition from Active State toPassive State occurs when there is no more need of unlicensed channel.

FIG. 10C outlines the operation in Active State, assuming LBE Option Brequirements.

As shown in the FIG. 10C, PHY checks the availability of unlicensedchannel and transmits (steps 1b, 2b, 3b and 6b), while MAC makes thescheduling decision and decides whether radio resources over unlicensedcarrier is needed (steps 4b and 7b). In addition, MAC also generatesbackoff counter N (step 5b).

It is worth pointing out that scheduling decision in 4b and 7b considersboth licensed and unlicensed channel resources. User data can bedirected for transmission on either licensed or unlicensed channel. WhenMAC evaluates the demand for unlicensed channel resources (steps 4b and7b), it may take PHY's need into consideration, e.g., whether DRS willbe transmitted soon. Step 3b includes not only the time eNB transmitsdata over the unlicensed channel, but also the idle period that isrequired to fulfil LBT requirements, as well as the short controlsignalling transmission duration. The initial CCA check (step 2b) istriggered by the demand for unlicensed channel resources, such as MACdata and/or PHY signalling. This is in line with “demand-driven”definition of LBE.

For ECCA check (steps 5b and 6b), MAC provides the backoff counter N andPHY is in charge of starting and performing CCA check in each of the NECCA slots. The reason of letting MAC but not PHY generate backoffcounter value N is that the MAC scheduler has the betterknowledge/prediction regarding the availability of data that may betransmitted or offloaded over unlicensed carrier(s). In addition, theknowledge of value N will help MAC scheduler predict buffering delay tosome extent. At the end of a failed ECCA and before PHY starts a newround of ECCA, it is reasonable for PHY to check with MAC first whetherthere is still any need to access the resources of unlicensed channel.If MAC scheduler prefers to use licensed carriers for data transmissionsin the next several subframes, or if MAC empties its buffer already,there is no point for PHY to start a new round of ECCA. Because of thenecessity of checking with MAC (step 4b) and the benefit of MAC knowingN value, it is preferred that MAC provides the backoff counter N to PHY.

FIG. 10D outlines the operation in Active State following FBErequirements. Interpretation of each step is similar to that in FIG.10C.

FIG. 11 is a diagram for signaling of buffer status and power-headroomreports.

UEs that already have a valid grant obviously do not need to requestuplink resources. However, to allow the scheduler to determine theamount of resources to grant to each terminal in future subframes,information about the buffer situation and the power availability isuseful, as discussed above. This information is provided to thescheduler as part of the uplink transmission through MAC controlelement. The LCID field in one of the MAC subheaders is set to areserved value indicating the presence of a buffer status report, asillustrated in FIG. 11.

The amount of transmission power available in each terminal is alsorelevant for the uplink scheduler. Obviously, there is little reason toschedule a higher data rate than the available transmission power cansupport. In the downlink, the available power is immediately known tothe scheduler as the power amplifier is located in the same node as thescheduler. For the uplink, the power availability, or power headroom (asdiscussed in Section 13.1.5), is defined as the difference between thenominal maximum output power and the estimated output power for UL-SCHtransmission.

This quantity can be positive as well as negative (on a dB scale), wherea negative value would indicate that the network has scheduled a higherdata rate than the terminal can support given its current poweravailability. The power headroom depends on the power-control mechanismand thereby indirectly on factors such as the interference in the systemand the distance to the base stations. Information about the powerheadroom is fed back from the terminals to the eNodeB in a similar wayas the buffer-status reports—that is, only when the terminal isscheduled to transmit on the UL-SCH.

A Power Headroom Report (PHR) shall be triggered if any of the followingevents occur: i) prohibitPHR-Timer expires or has expired and the pathloss has changed more than dl-PathlossChange dB for at least oneactivated Serving Cell of any MAC entity which is used as a pathlossreference since the last transmission of a PHR in this MAC entity whenthe MAC entity has UL resources for new transmission; ii)periodicPHR-Timer expires; iii) upon configuration or reconfiguration ofthe power headroom reporting functionality by upper layers, which is notused to disable the function; iv) activation of an SCell of any MACentity with configured uplink, v) addition of the PSCell, vi)prohibitPHR-Timer expires or has expired, when the MAC entity has ULresources for new transmission, and the following is true in this TTIfor any of the activated Serving Cells of any MAC entity with configureduplink: there are UL resources allocated for transmission or there is aPUCCH transmission on this cell, and the required power backoff due topower management for this cell has changed more than dl-PathlossChangedB since the last transmission of a PHR when the MAC entity had ULresources allocated for transmission or PUCCH transmission on this cell.

It is also possible to configure a prohibit timer to control the minimumtime between two power-headroom reports and thereby the signaling loadon the uplink.

If the MAC entity has UL resources allocated for new transmission forthis TTI the MAC entity shall start periodicPHR-Timer if it is the firstUL resource allocated for a new transmission since the last MAC reset.If the Power Headroom reporting procedure determines that at least onePHR has been triggered and not cancelled, the MAC entity shall obtainthe value of the Type 1 power headroom from the physical layer, andinstruct the Multiplexing and Assembly procedure to generate andtransmit a PHR MAC control element based on the value reported by thephysical layer. And the MAC entity start or restart periodicPHR-Timer,start or restart prohibitPHR-Timer, and cancel all triggered PHR.

For the uplink transmission, the UE uses the Power Headroom Reporting(PHR) in order to provide the network with information about thedifference between the nominal maximum transmit power and the estimatedrequired transmit power. Thus, PHR indicates how much transmission powercan be additionally used from the UE side.

In this sense, PHR trigger events are specified in the spec, whichtriggers PHR when there is a power situation change in the UE side.

In Rel-13, SI on LAA has been started in 3GPP, where unlicensed cell canbe used for data transmission unless it is occupied by others. As theunlicensed cell can be occupied by others from time to time, the UE maynot be able to transmit the data on the unlicensed cell even thoughthere is enough power to transmit data and the UE received an uplinkgrant. In this case, the power situation of the UE changes because theUE does not transmit data. However, in the eNB side, the eNB may not beable to know that the UE drops the transmission of the data even thoughthe eNB already provided an uplink grant to transmit the data.Accordingly, the eNB may not be able to know that there is additionalpower the UE can use. Therefore, the UE needs to inform the eNB of powersituation.

FIG. 12 is a conceptual diagram for transmitting a power headroomreporting in a carrier aggregation with at least one SCell operating inan unlicensed spectrum according to embodiments of the presentinvention.

In this invention, if the UE drops data transmission on a cell not dueto power limitation situation, the UE triggers the power headroomreporting. In detail, if the UE drops data transmission on an unlicensedcell even though the UE received an uplink grant to transmit the data onthe unlicensed cell, the UE triggers the power headroom reporting.

The eNB configures the UE with at least one unlicensed cell (S1201).When the UE receives an uplink grant to transmit data on an unlicensedcell from an eNB, the UE checks whether the unlicensed cell is occupiedby other transmitters or not before transmitting the data on theunlicensed cell (S1203).

The UE determines that the data is not to be transmitted using theuplink grant if the unlicensed cell is not available for transmittingdata (S1205). When the UE determines that the data is not to betransmitted, the UE triggers a PHR (S1207).

In detail, the UE PHY layer checks whether the cell is occupied by othertransmitters or not. If the cell is occupied by other transmitters, andif there is data to transmit on the unlicensed cell by using thereceived uplink grant, the UE PHY layer informs the UE MAC entity thatUE PHY layer drops data transmission on the unlicensed cell although theUE is not in power limited situation.

If the UE MAC entity receives an indication from the UE PHY layer thatthe UE PHY layer drops data transmission on the unlicensed cell, the MACentity triggers the PHR, generates the (Extended) PHR MAC CE (S1209),and transmits the generated PHR MAC CE to the eNB on the licensed cell(S1211). And the MAC entity doesn't generate a MAC PDU including thedata.

Additionally, the UE indicates that the UE informs that the PHR istriggered due to data transmission drop (S1213).

Conventionally, a data transmission drop was for reasons of power limit.When data is drop, the UE determines that the insufficient transmissionpower, and the UE trigger the PHR so that the UE inform the eNB of powersituation (i.e. change in path loss, since the last power headroomreport is larger than a (configurable) threshold).

Meanwhile, in case of LAA, data drop may occur because the LBTprocedure, as well as the power limit, as mentioned above. In case thatUE drops data transmission on an unlicensed cell even though the UE hasenough power to transmit the data, unless the PHR is triggered becausethere is no change of power status, the eNB may not be able to know thatthere is additional power the UE can use, as mentioned above. Accordingto this invention, the PHR can be triggered even though there is nopower change to transmit data and the UE received an uplink grant if thenotification of data transmission drop is received from lower layers.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from essential characteristics of the presentinvention. The above embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by the appended claims, not by the abovedescription, and all changes coming within the meaning of the appendedclaims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

1. A method for a User Equipment (UE) operating in a wirelesscommunication system, the method comprising: receiving, by a MediumAccess Control (MAC) entity, an uplink grant to transmit data on anunlicensed cell from an e-NodeB (eNB); checking, by the MAC entity,whether the unlicensed cell is available for transmitting the data usingthe uplink grant; determining, by the MAC entity, not transmitting thedata using the uplink grant if the unlicensed cell is not available fortransmitting data; and triggering, by the MAC entity, a Power HeadroomReporting (PHR) when the UE determines that the data is not to betransmitted.
 2. The method according to claim 1, wherein the UEdetermines that the data is not to be transmitted even if the UE hasenough power to transmit the data.
 3. The method according to claim 1,wherein that the UE determines that the data is to be transmitted or notincludes that a physical layer checks whether the unlicensed cell is notavailable for transmitting the data or not, and informs that thephysical layer drops the data transmission on the unlicensed cell to theMAC entity if the unlicensed cell is not available for transmitting thedata.
 4. The method according to claim 3, wherein when the MAC entityreceives information that the physical layer drops the data transmissionon the unlicensed cell, the MAC entity triggers the PHR.
 5. The methodaccording to claim 3, wherein when the MAC entity receives informationthat the physical layer drops the data transmission on the unlicensedcell, the MAC entity doesn't generate a MAC Protocol Data Unit (PDU)including the data.
 6. The method according to claim 1, furthercomprising: generating, by the MAC entity, a PHR MAC Control Element(CE) when the PHR is triggered.
 7. The method according to claim 1,further comprising: transmitting, by the MAC entity, a PHR MAC ControlElement (CE) on a licensed cell to the eNB.
 8. A User Equipment (UE)operating in a wireless communication system, the UE comprising: a RadioFrequency (RF) module; and a processor configured to control the RFmodule, wherein the processor is configured to receive an uplink grantto transmit data on an unlicensed cell from an eNB, to check whether theunlicensed cell is available for transmitting the data using the uplinkgrant, to determine not transmitting the data using the uplink grant ifthe unlicensed cell is not available for transmitting data, and totrigger a Power Headroom Reporting (PHR) when the UE determines that thedata is not to be transmitted.
 9. The UE according to claim 8, whereinthe UE determines that the data is not to be transmitted even if the UEhas enough power to transmit the data.
 10. The UE according to claim 8,wherein that the UE determines that the data is to be transmitted or notincludes that a physical layer checks whether the unlicensed cell is notavailable for transmitting the data or not, and informs that thephysical layer drops the data transmission on the unlicensed cell to aMedium Access Control (MAC) entity if the unlicensed cell is notavailable for transmitting the data.
 11. The UE according to claim 10,wherein when the MAC entity receives information that the physical layerdrops the data transmission on the unlicensed cell, the MAC entitytriggers the PHR.
 12. The UE according to claim 10, wherein when the MACentity receives information that the physical layer drops the datatransmission on the unlicensed cell, the MAC entity doesn't generate aMAC Protocol Data Unit (PDU) including the data.
 13. The UE according toclaim 8, wherein the processor is further configured to generate PHR MACControl Element (CE) when the PHR is triggered.
 14. The UE according toclaim 8, wherein the processor is further configured to transmit a PHRMAC Control Element (CE) on a licensed cell to the eNB.
 15. A method fora User Equipment (UE) operating in a wireless communication system, themethod comprising: receiving, by a Medium Access Control (MAC) entity,an uplink grant to transmit a MAC Protocol Data Unit (PDU) including aPower Headroom Reporting (PHR) MAC Control Element (CE) on an unlicensedcell from an e-NodeB (eNB); checking, by the MAC entity, whether theunlicensed cell is available for transmitting the MAC PDU using theuplink grant; determining, by the MAC entity, not transmitting the MACPDU using the uplink grant if the unlicensed cell is not available fortransmitting MAC PDU; and triggering, by the MAC entity, a PHR when theUE determines that the MAC PDU is not to be transmitted.